1. Field of the Invention
The present invention relates to communication content recording apparatus and method of recording communication contents such as speech data, etc. to be transmitted through a communication line.
2. Description of Related Art
Various dealings using telephone lines have been made in financial institutions such as banks, securities, etc., telephone marketing such as telephone-ordering and public undertakings such as horse racing, etc. In such a case, communication contents are usually required to be recorded in order to check them again or leave them as evidence. Therefore, communication content recording apparatuses for recording communication contents without affecting the persons using the telephonic communications have been hitherto utilized.
In this type of communication content recording apparatuses, the start and stop timings of a communication recording operation are controlled by surveying the signal level on a telephone line or surveying the off-hook/on-hook operation in order to record communication contents without affecting the operations of existing communication systems as in the case of DN-08R and DN-09R models produced by Nippon Columbia Co., Ltd., or Japanese Laid-open Patent Application No. Hei-5-234247.
Recent developments in digital technologies have promoted propagation of ISDN (Integrated Services Digital Network) as a communication network in which various different services such as telephonic communication services, data communication services, etc. can be connected by using the same digital exchanger and digital bus. ISDN transmits information while digitizing the information, and thus ISDN can perform higher-speed communications with less signal deterioration than analog lines. Here, ISDN will be briefly described.
ISDN has a signal channel (D channel) for transmitting control information such as call control information, etc. and an information channel (B channel) for transmitting user information. Two types of interface are provided as interfaces of ISDN. One is a basic interface (BRI: Basic Rate Interface) comprising one D channel and two B channels, and the other is a primary rate interface (PRI) comprising plural B channels and a D channel.
In a user/network interface (I interface) of ISDN, layer 1 to layer 3 are defined for the connection condition between a communication terminal unit and ISDN. The layer 1 to layer 3 are compliant with a 7-layer model serving as a basic reference model of Open System Interconnection (OSI) defined by ISO (International Standardization Organization), and based on basic layers of a physical layer, a data link layer and a network layer which are associated with control of communication networks, thereby enabling communications among various communication equipment.
The layer 1 is applied to an information channel and a signal channel, and an electrical/physical condition to connect a communication terminal unit to a digital line terminal unit (DSU: Digital Service Unit) is defined in the layer 1. In the layer 1 are specifically defined a wiring construction, a frame structure, a transmission path code, signal channel access control, frame synchronization, electrical characteristics, power supply conditions, etc.
In the layer 2, information transmission management for implementing transmission of information to be transmitted/received through a signal channel between a communication terminal unit and ISDN is defined. This is called LAPD (Link Access Procedure on the D-channel). By establishing the link between the communication terminal unit and ISDN in the layer 2, xe2x80x9ccallxe2x80x9d of the information channel can be established on the layer 3 as described later. Specifically, a frame format, a frame type, an information transmission procedure, a management procedure of a terminal endpoint identifier (TEI), etc. are defined. In the frame format, there are provided an information frame for carrying out information transmission in the layer 3, a surveying frame for checking transmission/reception of the information frame and making a re-transmission request, and an unnumbered frame.
FIG. 11 is a diagram showing the structure of an LAPD frame in ISDN. As shown in FIG. 11, a frame based on the LAPD protocol contains an address portion, a control portion (containing sequence number), an information portion and a frame check sequence portion for detecting an error, which are sandwiched between flags (0111110).
In the layer 3, information on an information channel, which is transmitted between communication terminal units after the link is established in the layer 2, is defined. Specifically, the content of the information format, the control of a line switching connection, a packet communication procedure, etc. are defined. The line connection and the link between ISDN (network) and each of communication terminal units are established by the layers 1 and 2, and xe2x80x9ccallxe2x80x9d between communication terminal units through ISDN is established by the layer 3.
In the layer 3, messages indicating call control, etc. are transmitted on the basis of the information frame. As messages indicating the call control, there are provided a call-setup message, a call proceeding (call-setup reception) message, an alerting message, a connect message and a connect acknowledge message, which are to establish a call, and disconnect, release and release complete messages, which are to release the call.
Next, the frame format used in ISDN will be described.
A transmission sequence number and a reception sequence number are affixed to an information frame. Each of these sequence numbers is incremented one by one when transmitted or received. Each of the transmission and reception sequence numbers is modulo (mod) 128 in which numerical values of 0 to 127 are repeatedly used (for example, 0, 1, 2, . . . 126, 127, 0, 1, 2, . . . ). For example, an information frame which is first transmitted is allotted with a transmission sequence number xe2x80x9c0xe2x80x9d, and an information frame which is secondly transmitted is allotted a transmission sequence number xe2x80x9c1xe2x80x9d. At this time, if the reception side has not yet received any information frame, the reception sequence number of an information frame transmitted by the reception side is equal to xe2x80x9c0xe2x80x9d. If the reception side receives an information frame, the reception sequence number of an information frame transmitted by the reception side is equal to xe2x80x9c1xe2x80x9d.
As the surveying frame, there are provided a reception ready (RR) frame for notifying the transmission sequence number of a frame to be next received (the number of frames which have been received) to a communication partner with which communications are being made when no information frames have been generated for a predetermined time period, and a reject (REJ) frame for detecting, on the basis of the transmission sequence number of the frame thus received, a frame which could not be received due to a transmission error, and requesting re-transmission of the missing frame. Like the information frame, a reception sequence number is also affixed to the surveying frame. In the case of the RR frame, it represents the transmission sequence number of a frame to be next received (the number of frames which have been received), and in the case of the REJ frame, it represents the transmission sequence number of a frame which could not be received due to a transmission error.
As the unnumbered frame, there are provided a set asynchronous balanced mode extended (SABME) frame, an unnumbered information (UI) frame, a disconnect (DISC) frame, an unnumbered acknowledgment (UA) frame, etc.
Next, a conventional communication system using ISDN will be described.
FIG. 12 is a schematic diagram showing a conventional communication system using ISDN.
As shown in FIG. 12, a communication terminal unit 503 is connected to ISDN 502 through DSU 504. DSU 504 performs a control operation to physically connect the communication terminal unit 503 and ISDN 502. The communication terminal unit 503 includes a receiver 505, an LAPD reception processor 506, a transmitter 507, an LAPD transmission processor 508, a layer 3 protocol processor 509 and an information channel processor 510 for processing data on the information channel.
The receiver 505 receives information (data) transmitted through DSU 504 from ISDN 502. It outputs the data on the signal channel to the LAPD reception processor 506 and also outputs the data on the information channel to the information channel processor 510.
The LAPD reception processor 506 obtains a frame format, a frame type, information transmission procedure, etc. from the LAPD frame on the signal channel to manage information received/transmitted through the signal channel.
The LAPD reception processor 506 performs error detection on the basis of a frame check sequence portion of an LAPD frame, and also surveys continuity of transmission sequence numbers of LAPD frames received to thereby perform defect detection of the LAPD frames. When an error is detected or an LAPD frame has a defect, the LAPD transmission processor 508 transmits a re-transmission request through the transmitter 507 to ISDN 502.
The layer 3 protocol processor 509 surveys the communication status between the communication terminal unit 503 thereof and ISDN 502 to control communications with ISDN 502 on the basis of messages such as call-establishment, call-release, etc. For example, when information is transmitted to a communication partner, the LAPD transmission processor 508 and the transmitter 507 are controlled so that control information is generated and transmitted together with information generated in the information channel processor 510.
In the conventional communication system using ISDN thus constructed, messages are communicated on the signal channel between the communication terminal unit 503 and ISDN 502 to perform establishment or release of call of an information channel or selection of an information channel. When an error is detected in the communication of a message, the system is restored from the error by re-transmitting the message.
FIG. 13 is a flowchart showing the processing in the above conventional communication system using ISDN when a communication terminal unit receives an error frame.
When an error occurs in the data transmission from ISDN 502 to the communication terminal unit 503 or from the communication terminal unit 503 to ISDN 502 in FIG. 12, the processing is carried out according to the flow shown in FIG. 13.
In a case of the signal channel for performing the data transmission from ISDN 502 to the communication terminal unit 503, when the receiver 505 receives an LAPD frame (step S701), the LAPD reception processor 506 first judges whether or not the LAPD frame received is an error frame (step S702). If the LAPD frame received is not any error frame, the processing is carried out according to the content of the LAPD frame (step S703).
On the other hand, if the LAPD frame is an error frame, the error frame is discarded (step S704). The LAPD transmission processor 508 transmits a re-transmission request through the transmitter 507 to ISDN 502 (step S705). The LAPD reception processor 506 neglects information which has been received during a time period from the reception of the error frame until the transmission of the re-transmission request. ISDN 502 receiving the re-transmission request re-transmits the information indicated by the re-transmission request as an LAPD frame.
As described above, the LAPD reception processor 506 surveys the continuity of the transmission sequence numbers of the received LAPD frames to detect defectiveness of the LAPD frames. If there is any defect, the LAPD transmission processor 508 transmits a re-transmission request as in the case of the error frame. The same processing is carried out in ISDN 502 in the case of the signal channel for performing the data transmission from the communication terminal unit 503 to ISDN 502.
FIG. 14 shows an example of the processing procedure carried out between the communication terminal unit 503 and ISDN 502 according to the flow of FIG. 13. In this case, the communication terminal unit 503 judges that information B is an error frame, and transmits a re-transmission request message to ISDN 502. The communication terminal unit 503 neglects frames (information pieces C, D) which have been received during the time period from reception of an error frame until reception of a frame (information A) based on the re-transmission request.
Such re-transmission control is defined by ITU-TS Recommendation I.441 (Q.921). Others are disclosed in Japanese Laid-open Patent Application No. Hei-5-183644, Japanese Laid-open Patent Application No. Hei-7-143147, and Japanese Laid-open Patent Application No. Hei-9-200290.
The conventional communication content recording apparatus records communications which are carried out through analog lines, and it does not support a digital communication in which connection setting is carried out according to a protocol like ISDN as described above. That is, in the conventional communication content recording apparatus in which the start and stop of the communication recording are controlled by surveying the signal level on the line and on-hook/off-hook, it is difficult to control communication data such as speech data, etc. to be reliably recorded in digital communications with which various services such as telephonic communications, data communications, etc. are supplied.
Further, as described above, in communication based on LAPD between communication terminal unit and ISDN, when one communication terminal unit or ISDN receives an error frame, the communication terminal unit or ISDN (which receives the frame concerned) makes a re-transmission request to the communication terminal unit or ISDN so that the frame can be re-transmitted from the communication terminal unit or ISDN.
On the other hand, the communication content recording apparatus is set so that the transmission to ISDN is inhibited to prevent the communication content recording apparatus from affecting concerned parties using the telephonic communications, as described above. That is, in the communication content recording apparatus, only the receiver for receiving communication data such as speech data, etc. from ISDN is provided as an interface of ISDN.
Therefore, there is a possibility that communication will be performed correctly between communication terminal units, but the communication content recording apparatus for recording a communication content between the communication terminal units concerned will receive an error frame for some reason, so that the communication data cannot be correctly recorded when the error frame is a frame indicating the start or end of the recording.
The present invention has been implemented in view of the above situation, and has an object to provide a communication content recording apparatus which can support digital communications such as ISDN, etc.
Further, the present invention has another object to provide a digital-communication-capable communication content recording apparatus which can record communication data correctly even when an error frame is received or a frame is missing.
In order to achieve the above objects, according to a first aspect of the present invention, a communication content recording apparatus for recording the contents of communications which are carried out between communication terminal units through a digital communication network, includes:
receiving means for receiving data on a signal channel and data on an information channel which are received/transmitted between the digital communication network and the communication terminal units;
protocol processing means for extracting frames from the data on the signal channel received by the receiving means according to a protocol and processing the frames;
information channel processing means for processing the data on the information channel received by the receiving means so that the processed data can be recorded; and
protocol controlling means for controlling the start and stop of the processing of the information channel processing means on the basis of a processing result of the protocol processing means.
According to the communication content recording apparatus of the first aspect of the present invention, the start/stop operation of the processing for converting the data on the information channel to recordable data is controlled according to the processing result in the protocol processing means for the frame on the signal channel received by the receiving means. With this operation, for example, when the received frame on the signal channel contains a message for call establishment, the processing for converting the data on the information channel to the recordable data can be started, and when it contains a message for call release, the conversion processing concerned can be stopped. Accordingly, in communications through a digital communication network, the communication content can be recorded without affecting concerned parties in communication with each other.
In the first aspect of the present invention, when a processing result of the protocol processing means indicates that the frame received is an error frame, the protocol controlling means may be designed to presume the content of the error frame on the basis of a processing result of the protocol processing means for a frame received immediately before the error frame if the reception means does not receive a next frame within a predetermined time lapse after receiving the error frame, or according to a processing result of the protocol processing means for the next frame. With this operation, the communication content can be normally recorded even when an error frame is received.
For example, when an error frame is received because of occurrence of troubles between communication terminal units in communication, the communication terminal unit at the frame reception side also receives an error frame. Therefore, a re-transmission-request frame is transmitted from the communication terminal unit concerned or the digital communication network to the digital communication network or the communication terminal unit at the frame transmission side. Accordingly, when the frame received subsequent to the error frame is a re-transmission-request frame, the frame which was judged to be the error frame is re-transmitted from the digital communication network or the communication terminal units at the frame transmission side. Therefore, the error frame can be merely discarded.
However, when an error frame is received although the normal communication is performed correctly between the communication terminal units in communication, the re-transmission-request frame is not transmitted from the communication terminal unit or the digital communication network at the frame reception side to the digital communication network or the communication terminal unit at the frame transmission side. Therefore, there may arise such a case that merely discarding the error frame cannot have the communication content be correctly recorded when the error frame contains a message for call establishment or call release.
Therefore, in a case where a processing result of the protocol processing means indicates the error frame, the start/stop of the recording of the communication data can be performed correctly by presuming the content of the error frame from a processing result of the frame received immediately before the error frame at the protocol processing means if the receiving means does not receive a next frame within a predetermined time period after receiving the error frame or the frame which is received subsequently to the error frame by the reception means is not a re-transmission-request frame.
Further, according to a second aspect of the present invention, a communication content recording apparatus for recording the content of communications which are carried out between communication terminal units through a digital communication network, includes:
receiving means for receiving data on a signal channel and data on an information channel which are received/transmitted between the digital communication network and the communication terminal units;
frame processing means for extracting frames from the data on the signal channel received by the receiving means and outputting the extracted frames;
information channel processing means for processing the data on the information channel received by the receiving means so that the processed data are recordable;
protocol controlling means for controlling the start/stop of the processing of the information channel processing means according to a message contained in a frame output from the frame processing means; and
frame missing detection means for surveying continuity of frames output from the frame processing means to detect frame missing, wherein the protocol controlling means controls the start/stop of the processing of the information channel processing means for the information channel concerned in accordance with the progress of a call establishment or call release procedure of the information channel when the frame missing is detected by the frame missing detection means.
According to the second aspect of the present invention, the continuity of the frames which are communicated on the signal channel are monitored, and when a frame missing occurs, the start/stop of the processing of the information channel processing means for the information channel is controlled in accordance with the progress of the call establishment or call release of the information channel which is defined in the protocol between the communication terminal unit and the digital communication network. With this operation, even when a frame missing occurs, the start/stop of the recording of the communication content can be performed correctly.
In the second aspect of the present invention, when a frame extracted from the data on the signal channel received by the receiving means is an error frame, the frame processing means may discard the frame concerned without delivering it to the protocol controlling means. With this operation, the treatment of the frame missing and the error frame can be performed according to the same procedure with no discrimination therebetween so that the start/stop of the recording of the communication content can be performed correctly.